Air conditioner and control system therefor

ABSTRACT

An air conditioner includes: a compressor configured to compress a refrigerant; an outside heat exchanger configured to make the compressed refrigerant radiate heat; a pressure reducing unit configured to reduce the pressure of the heat-radiated refrigerant; an inside heat exchanger configured to vaporize the pressure-reduced refrigerant; a discharge pressure detector configured to detect a discharge pressure of the refrigerant discharged from the compressor; a controller configured to provide a duty factor according to the detected discharge pressure; and a control valve configured to adjust a discharge capacity of the compressor according to the provided duty factor. During a start-up operation of the compressor, the controller controls the duty factor provided to the control valve so that the discharge pressure detected by the discharge pressure detector is maintained within a predetermined range and so that the duty factor reaches a maximum system duty factor.

CROSS REFERENCE TO RELATED APPLICATIONS AND INCORPORATION BY REFERENCE

This application is based on and claims the benefit of priority from theprior Japanese Patent Application No. 2005-133298 filed on Apr. 28,2005; the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an air conditioner having arefrigeration cycle that uses a supercritical fluid as a refrigerant.

2. Description of the Related Art

A refrigeration cycle generally drives a compressor to a full-strokestate in a short period of time in a start-up operation, to quicklystabilize the refrigeration cycle.

Some recent air conditioners for vehicles have a refrigeration cyclethat uses a supercritical fluid, such as a carbon dioxide gas as arefrigerant. The supercritical fluid refrigerant has a reduced affect tocontribute to global warming.

Under a high heat load at an ambient temperature of 40° C. or higher,the refrigeration cycle using a the supercritical fluid refrigerantgenerally shows an equilibrium state at a pressure of about 8 to 11 Mpa,even when the refrigeration cycle is stopped. If the refrigeration cycleis started in this state, a discharge pressure of the compressor on thehigh-pressure side of the refrigeration cycle suddenly increases and maydamage components of the refrigeration cycle.

To avoid this problem, the related art (for example, Japanese UnexaminedPatent Application Publication No. 2002-61968) discloses a vehicle airconditioner. Therein, if a heat load (for example an ambienttemperature) is greater than a predetermined value upon start-up of thecompressor, a duty factor set for an electrical control valve thatcontrols a discharge capacity of the compressor is reduced, and drivesthe compressor for a predetermined time with the reduced duty factor.Thereafter, the reduced duty-factor is switched to a normal controloperation. When a heat load is high, the related art can start acompressor without a sudden excessive increase of the discharge pressureof the compressor.

SUMMARY OF THE INVENTION

The above-mentioned related art, however, always spends thepredetermined start-up time whenever a heat load is high, without regardto the condition of the refrigerant in the refrigeration cycle.

The present invention was developed, based on the fact that, after along stoppage, a refrigerant in a refrigeration cycle is in anequilibrium state and there is no pressure difference between inlet anddischarge pressures of a compressor and that, after a short stoppage, apressure difference remains between inlet and discharge pressures of thecompressor.

An object of the present invention is to provide an air conditionercapable of preventing a discharge pressure from excessively increasingduring a start-up operation and minimizing a start-up time.

An aspect of the present invention provides an air conditioner includinga compressor configured to compress a refrigerant, an outside heatexchanger configured to make the compressed refrigerant radiate heat, apressure reducing unit configured to reduce the pressure of theheat-radiated refrigerant, an inside heat exchanger configured tovaporize the reduced pressure refrigerant, a discharge pressure detectorconfigured to detect a discharge pressure of the refrigerant dischargedfrom the compressor, a controller configured to provide a duty factoraccording to the detected discharge pressure, and a control valveconfigured to adjust a discharge capacity of the compressor according tothe provided duty factor. The controller is operative, during a start-upoperation of the compressor, to control the duty factor provided to thecontrol valve so that the discharge pressure detected by the dischargepressure detector is maintained within a predetermined range, and sothat the duty factor goes to a maximum system duty factor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing an air conditioner according to anembodiment of the present invention;

FIG. 2 is a sectional view showing a compressor of the air conditionerof FIG. 1;

FIG. 3 is a schematic view showing an electrical control valve of thecompressor of FIG. 2;

FIG. 4 is a graph showing a relationship between a duty factor and adischarge capacity;

FIG. 5 is a flowchart showing steps of setting a duty factor with acontrol amplifier during a start-up operation; and

FIG. 6 is a graph showing the relationship between a start-up time, aduty factor, and a discharge pressure.

DETAILED DESCRIPTION OF EMBODIMENTS

An air conditioner according to an embodiment of the present inventionwill be explained. The air conditioner of this embodiment has arefrigeration cycle that uses a supercritical fluid, e.g., a carbondioxide gas, as a refrigerant.

FIG. 1 is a schematic view showing the air conditioner according to theembodiment. In FIG. 1, the air conditioner is a vehicle air conditionerinstalled in the vehicle 1 and includes the refrigeration cycle 100 thatcirculates a carbon dioxide gas, as a refrigerant, and conducts heatexchange between the refrigerant and air.

The refrigeration cycle 100 includes a variable capacity compressor 101,an outside heat exchanger 102, a pressure reducing unit 103, an insideheat exchanger 104, and an accumulator 105. The components 101 to 105are connected in series through conduits. The compressor 101 supplieskinetic energy to the refrigerant so that the refrigerant issuccessively circulated through the components 101 to 105.

The compressor 101 is arranged outside of a passenger compartment of thevehicle 1. For example, the compressor 101 is arranged in an enginecompartment. A vehicle engine 106 generates torque, which is transmittedthrough a belt 115 to the compressor 101, to drive the compressor 101.The compressor 101 takes in a low-pressure gaseous refrigerant from theaccumulator 105, compresses the refrigerant, and discharges ahigh-temperature, high-pressure gaseous refrigerant to the outside heatexchanger 102.

The outside heat exchanger 102 is arranged outside the passengercompartment and radiates heat of the high-temperature, high-pressuregaseous refrigerant discharged from the compressor 101 to outside air.The outside heat exchanger 102 is provided with a blower, such as anelectric fan, to blow outside air toward the outside heat exchanger 102.Heat is exchanged between the refrigerant passing through the outsideheat exchanger 102 and the outside air, to dissipate the heat of therefrigerant.

The pressure reducing unit 103 receives the high-pressure gaseousrefrigerant from the outside heat exchanger 102, reduces the pressurethereof, i.e., expands the volume thereof, and provides alow-temperature, low-pressure misty refrigerant.

The inside heat exchanger 104 is arranged in an air conditioning duct108. In the duct 108, an air conditioning fan 109 generates an airconditioning air flow. Heat of the air flow is absorbed by thelow-temperature, low-pressure misty refrigerant supplied from thepressure reducing unit 103 and passed through the inside heat exchanger104. Namely, the refrigerant passing through the inside heat exchanger104 evaporates to take heat away from the air flow passing through theduct 108. The heat-deprived air flow in the duct 108 is dehumidified tobe a cool air flow, which is blown through an outlet 108 a into thepassenger compartment.

The accumulator 105 separates the refrigerant discharged from the insideheat exchanger 104 into a gas and a liquid. The separated liquidrefrigerant is accumulated and the separated gaseous refrigerant issupplied to the compressor 101.

FIGS. 2 and 3 show details of the compressor 101.

The compressor 101 is a swash plate-type compressor that has a swashplate 137 and is capable of changing the piston stroke corresponding tothe inclination angle of the swash plate 137.

In FIG. 2, the compressor 101 includes a housing 121. The housing 121accommodates cylinder bores 123, a suction chamber 127 communicatingthrough a suction hole 125 with a top dead center side of the cylinderbore 123, a discharge chamber 131 communicating through a discharge hole129 with the top dead center side of the cylinder bore 123, and acrankcase 133 communicating with a bottom dead center side of eachcylinder bore 123. The housing 121 supports a rotatable drive shaft 135in the crankcase 133. In the crankcase 133, the swash plate 137 isconnected to the drive shaft 135 and is inclinable relative to the driveshaft 135. The cylinder bore 123 accommodates a piston 141 that isslidable therein and is linked through a piston rod 139 with the swashplate 137. Outside the housing 121, a pulley 143 is integral with thedrive shaft 135.

When the drive shaft 135 rotates, the swash plate 137 oscillates in anaxial direction of the cylinder bore 123, so that the piston 141reciprocates in the cylinder bore 123. In response to the reciprocationof the piston 141, a low-pressure refrigerant in the suction chamber 127is drawn into the cylinder bore 123 and is compressed in the cylinderbore 123. The compressed high-pressure refrigerant is discharged intothe discharge chamber 131.

As used herein, “Ps” is the pressure of a refrigerant on low-pressureside of the refrigeration cycle which introduced into the compressor 101and corresponds to a pressure in the suction chamber 127. “Pd” is thepressure of a refrigerant on high-pressure side of the refrigerationcycle which discharged from the compressor 101 and corresponds to apressure in the discharge chamber 131. “Pc” is a pressure in thecrankcase 133 of the compressor 101.

In the compressor 101, the piston 141 receives, as a back pressure, apressure Pc of the crankcase 133. Controlling the pressure Pc adjusts apressure difference (Pc−Ps) acting on the piston 141. Adjusting thepressure difference changes an inclination of the swash plate 137relative to the drive shaft 135, thereby changing the piston stroke,i.e., the discharge capacity of the compressor 101.

To adjust the pressure Pc of the crankcase 133, the compressor 101includes: a pressure purging path 152 that connects the crankcase 133and suction chamber 127 to each other to always purge the pressure ofthe crankcase 133 to the suction chamber 127; a pressure introducingpath 154 that connects the crankcase 133 and discharge chamber 131 toeach other to introduce a pressure Pd of the discharge chamber 131 intothe crankcase 133; and an electric control valve (hereinafter referredto as “ECV”) 107 that opens and closes the pressure introducing path154.

The ECV 107 is, for example, a solenoid valve whose opening iscontrolled in response to an external electrical signal. The externalelectric signal (control signal) is supplied from a control amplifier111 as a controller to the ECV 107 to adjust the opening of the ECV 107and introduce/stop the high pressure Pd from the discharge chamber 131into the crankcase 133 through the pressure introducing path 154. As aresult, the pressure Pc in the crankcase 133 can be controlled. Thecontrol operation will change the pressure difference (Pc−Ps) betweenthe crankcase 133 and the suction chamber 127, i.e., a pressure balanceacting on the piston 141, thereby changing the inclination of the swashplate 137. Consequently, the piston stroke is changed so as to changethe refrigerant discharge capacity of the compressor 101. The controlsignal from the control amplifier 111 to the ECV 107 sets a duty factor.The duty factor determines an opening (open time or open area) of theECV 107 that determines a discharge capacity of the compressor 101.

FIG. 4 is a graph showing a relationship between a duty factor anddischarge capacity of the compressor. As the duty factor increases, therefrigerant discharge capacity of the compressor 101 increases. Morespecifically, increasing the duty factor reduces the opening of thepressure introducing path 154 to reduce the flow rate of a high-pressurerefrigerant passing through the pressure introducing path 154, decreasethe pressure Pc in the crankcase 133, decrease the pressure difference(Pc−Ps), increase the piston stroke, and expand the discharge capacityof the compressor 101. On the other hand, reducing the duty factorincreases the opening of the pressure introducing path 154, to increasethe flow rate of a high-pressure refrigerant passing through thepressure introducing path 154, increase the pressure Pc in the crankcase133, increase the pressure difference (Pc−Ps), reduce the piston stroke,and decrease the discharge capacity of the compressor 101.

If the duty factor is set to a minimum system duty factor of 0%, thehigh pressure Pd in the discharge chamber 131 is applied into thecrankcase 133, to increase the pressure Pc in the crankcase 133,maximizes the inclination of the swash plate 137 relative to the driveshaft 135 (substantially at a right angle), destrokes the piston 141,i.e., the stroke of the piston 141 goes to zero, thereby minimizing thedischarge capacity of the compressor 101.

If the duty factor is set to a maximum system duty factor of 100%, thedischarge chamber 131 does not introduce any pressure into the crankcase133. As a result, the pressure Pc in the crankcase 133 decreases tominimize (about 45 degrees in this embodiment) the inclination of theswash plate 137 relative to the drive shaft 135 permit full strokemovement of the piston 141, thereby maximizing the discharge capacity ofthe compressor 101.

The maximum system duty factor is preset to permit full stroke movementof the piston 141, but the duty factor, is not limited to 100%. Themaximum system duty factor is dependent on the characteristics of thecompressor 101 and ECV 107 and may be about 80% or other appropriatepercentage.

A correlation between a duty factor and a pressure difference (Pd−Ps) ofthe compressor 101 is similar to that between the duty factor and adischarge capacity, and therefore, the ordinate of FIG. 4 may beconsidered as the pressure difference (Pd−Ps) of the compressor 101.

An example of the operation of the control amplifier (controller) 111will be explained in detail.

As shown in FIG. 1, on a discharge side (high-pressure side) of thecompressor 101, a discharge pressure sensor (discharge pressuredetector) 110 is provided for detecting a refrigerant discharge pressurePd of the compressor 101. The detected discharge pressure Pd istransmitted to the control amplifier 111.

The control amplifier (controller) 111 includes a Pd detector 112 forreceiving a signal indicative of the discharge pressure Pd from thedischarge pressure sensor 110, an ECV duty controller 113 for setting aduty factor for the ECV 107 according to the discharge pressure Pd, andan ECV adjuster 114 for transmitting an electrical signal to the ECV 107according to the set duty factor.

The control amplifier 111 may be a microcomputer including a CPU, a ROM,a RAM, I/O ports, and the like. According to a control program stored inthe ROM, the control amplifier 111 determines a duty factor for the ECV107 and outputs an electrical signal representative of the duty factor.

Control of the refrigeration cycle 100 according to the embodiment willbe explained. FIG. 5 is a flowchart showing steps carried out by thecontrol amplifier 111 when setting a duty factor for the ECV 107 at thestart of the compressor 101. When a driver of the vehicle, which usesthe refrigeration cycle 100, turns on an AC (air conditioner) switch ona control panel of the air conditioner, the steps of FIG. 5 start.

In step S101, the ECV duty controller 113 of the control amplifier 111checks to see if the compressor switch SW is ON. If it is not ON, theECV duty controller 113 sets a duty factor of 0% and transmits it to theECV adjuster 114 in step S102. Then, the ECV adjuster 114 transmits anelectrical signal to the ECV 107 with an electric signal representativeof the duty factor of 0%.

If the compressor switch is ON in step S101, the ECV duty controller 113determines, in step S103, whether or not start-up control is beingcarried out. If the start-up control is not being carried out, normalcontrol is started in step S104. The discharge capacity of thecompressor 101 is controlled so that a temperature set by the driver,through the control panel, is attained.

If the start-up control is in operation in step S103, step S105determines whether or not the refrigerant discharge pressure Pd,detected by the Pd detector 112, is less than a first set value of 12.5Mpa. If the discharge pressure Pd is below 12.5 Mpa, the ECV dutycontroller 113 increases, in step S106, a duty factor supplied to theECV adjuster 114 at a predetermined rate (for example, 1%/sec). Based onthe increased duty factor, the ECV adjuster 114 transmits an electricalsignal to the ECV 107.

In step S107, the ECV duty controller 113 checks to see if the dutyfactor provided to the ECV adjuster 114 is equal to a maximum systemduty factor. If it is not equal to the maximum system duty factor, stepS105 is again carried out. Thereafter, the duty factor is againincreased by the predetermined rate if a detected discharge pressure Pdis less than 12.5 Mpa. These steps are repeated until the duty factorprovided to the ECV adjuster 114 reaches the maximum system duty factor.

If the duty factor provided to the ECV adjuster 114 is equal to themaximum system duty factor in step S107, the start-up control isterminated in step S108, and step S101 is again carried out. In thiscase, step S103 determines that the start-up control is not beingcarried out, and therefore, the normal control operation is started instep S104.

If the discharge pressure Pd is not less than 12.5 Mpa in step S105,step S109 checks to see if the discharge pressure Pd is equal to orgreater than a second set value of 13 Mpa. According to this embodiment,the second set value of 13 Mpa is an upper limit set for the dischargepressure Pd. If the discharge pressure Pd of the compressor 101 isgreater than the upper limit, the discharge pressure Pd is abnormal. Thedischarge pressure Pd, however, must be high to some extent.Accordingly, the embodiment sets the value of 12.5 Mpa as a lower limitfor the discharge pressure Pd. More specifically, the control amplifier111 increases/decreases the duty factor of the ECV 107 so that thedischarge pressure Pd of the compressor 101 is maintained within therange of 12.5 to 13 Mpa.

If step S109 determines that the discharge pressure Pd is equal to orgreater than 13 Mpa, in step S110 the duty factor provided to the ECVadjuster 114 is decreased at a predetermined rate (for example, 1%/sec).The ECV adjuster 114 provides the ECV 107 with an electrical signal,based on the decreased duty factor.

If step S109 determines that the discharge pressure Pd is below 13 Mpa,i.e., if the discharge pressure Pd is within the range of 12.5 to 13Mpa, no adjustment is made on the duty factor provided to the ECVadjuster 114 and step S103 is carried out.

FIG. 6 is a graph showing variations in the discharge pressure Pdaccording to the above-described control. The graph of FIG. 6 shows arelationship between an elapsed time from the start of the compressor101, a duty factor, and the discharge pressure Pd.

At the start of the compressor 101, the embodiment increases the dutyfactor of the ECV 107 by a predetermined rate if the discharge pressurePd of the compressor 101 is below 12.5 Mpa and decreases the duty factorby a predetermined rate if the discharge pressure Pd is equal to orgreater than 13 Mpa. Accordingly, the embodiment can maintain thedischarge pressure Pd of the compressor 101 in a relatively highpressure range close to the upper limit and can increase the duty factorof the ECV 107 up to a maximum system duty factor.

The discharge pressure Pd of the compressor 101 will be high if thecompressor 101 is started shortly after stoppage. On the other hand, thedischarge pressure Pd will be low if the compressor 101 is started along period of time after stoppage. The embodiment can decrease thestart-up time of the former case to be less than that of the lattercase. The embodiment can maintain the discharge pressure Pd of thecompressor 101 within a predetermined range until the ECV 107 providefor a full stroke of the piston. Namely, the embodiment can ensure asufficient discharge capacity required for starting the compressor 101and can safely decrease a start-up time of the compressor 101.

When the discharge pressure Pd of the compressor 101 is within thepredetermined range, the embodiment does not increase or decrease theduty factor of the ECV 107. If the duty factor of the ECV 107 isincreased when the discharge pressure Pd is within the predeterminedrange, the discharge pressure Pd will suddenly increase and may damagecomponents of the refrigeration cycle 100. The embodiment can preventsuch a sudden increase in the discharge pressure Pd.

In this way, the embodiment can properly control a start-up time of thecompressor 101 according to a start-up load of the compressor 101.

Effect of this embodiment will be explained below.

The air conditioner according to this embodiment includes a compressor101 configured to compress a refrigerant, an outside heat exchanger 102configured to exchange heat of the compressed refrigerant, a pressurereducing unit 103 configured to reduce the pressure of theheat-exchanged refrigerant, an inside heat exchanger 104 configured tovaporize the pressure-reduced refrigerant, a discharge pressure detector110 configured to detect a discharge pressure of the refrigerantdischarged from the compressor 101, a controller 111 configured toprovide a duty factor according to the detected discharge pressure, anda control valve 107 configured to adjust the discharge capacity of thecompressor 101 according to the provided duty factor. The controller 111controls, during a start-up operation of the compressor 101, the dutyfactor provided to the control valve 107 so that the discharge pressuredetected by the discharge pressure detector 110 is maintained within apredetermined range and so that the duty factor reaches a maximum systemduty factor.

If the pressure of the low-pressure side of the refrigeration cycle 100is low and that of the high-pressure side thereof is high when startingthe compressor 101 in a certain ambient temperature, the compressor 101requires a small start-up load. If the low-pressure side andhigh-pressure side of the refrigeration cycle 100 are in an equilibriumstate when starting the compressor 101 in the same ambient temperature,the compressor 101 requires a heavy start-up load. In the former case,the embodiment can decrease the start-up time of the compressor 101 andcan more quickly achieve a full-stroke state than in the latter casewithout excessively increasing the discharge pressure of the compressor101.

To achieve this, the embodiment does not need a data map indicating anoptimum time dependent duty factors corresponding to heat load (forexample ambient temperatures around the heat exchanger 102, 104).Namely, the embodiment does not create a risk of an unforeseen incidentdue to a lack of data in such data map, and therefore, can safelycontrol a start-up operation of the compressor 101.

During the start-up operation of the compressor 101, the controller 111increases the duty factor of the control valve 107 at a predeterminedrate if the discharge pressure detected by the discharge pressuredetector 110 is less than a first set value and decreases the dutyfactor at a predetermined rate if the detected discharge pressure isequal to or greater than a second set value that is greater than thefirst set value.

During the start-up operation of the compressor 101, the controller 111maintains the duty factor of the control valve 107 if the detecteddischarge pressure is equal to or greater than the first set value andless than the second set value.

If the duty factor is increased when the discharge pressure of thecompressor 101 is within the predetermined range, the discharge pressurewill suddenly increase and may damage the components of therefrigeration cycle 100. The embodiment can prevent such a suddenincrease in the discharge pressure of the compressor 101.

Although the present invention has been described above by reference tocertain embodiments, the present invention is not limited to theseembodiments. Modifications and variations of the embodiments can be madewithout departing from the spirit or scope of the appended claims. Theembodiments are only for illustrative purposes and are not intended tolimit the present invention.

1. An air conditioner comprising: a compressor configured to compress arefrigerant; an outside heat exchanger configured to exchange heat ofthe compressed refrigerant; a pressure reducing unit configured toreduce the pressure of the heat-exchanged refrigerant; an inside heatexchanger configured to vaporize the reduced pressure refrigerant; adischarge pressure detector configured to detect a discharge pressure ofthe refrigerant discharged from the compressor; a controller configuredto set a duty factor in accordance with the detected discharge pressure;and a control valve configured to adjust a discharge capacity of thecompressor in accordance with the duty factor, the controllercontrolling, during a start-up operation of the compressor, the dutyfactor provided to the control valve so that the discharge pressuredetected by the discharge pressure detector is maintained within apredetermined range and so that the duty factor goes to a maximum systemduty factor.
 2. The air conditioner of claim 1, wherein: during thestart-up operation of the compressor, the controller increases the dutyfactor at a predetermined rate when the detected discharge pressure fromthe discharge pressure detector is less than a first set value anddecreases the duty factor at a predetermined rate when the detecteddischarge pressure is equal to or greater than a second set value thatis greater than the first set value.
 3. The air conditioner of claim 2,wherein: during the start-up operation of the compressor, the controllermaintains the duty factor provided to the control valve when thedetected discharge pressure from the discharge pressure detector isequal to or greater than the first set value and less than the secondset value.
 4. The air conditioner of claim 1, wherein: the airconditioner is a vehicle air conditioner installed in a vehicle (1); andthe compressor is driven by an engine of the vehicle (1).
 5. Acontroller for controlling a control valve that adjusts a degree ofopening of a pressure introducing path connecting a discharge chamberand crankcase of a compressor to each other, the controller configuredto: provide a control signal to the control valve, the control signalrepresenting a duty factor that determines the degree of opening of thepressure introducing path; and provide the control signal, during astart-up operation of the compressor, to attain a maximum system dutyfactor and maintain a discharge pressure of a refrigerant dischargedfrom the compressor within a predetermined range.